The invention relates to a microfluidic circuit comprising at least one component capable of acting on a fluid present in the circuit, in particular to create a flow of the fluid in the circuit, to block the flow, to direct and steer the flow, and/or to mix the fluid with another fluid, amongst other possibilities.
The microfluidics devices present a certain number of technical problems that have not been solved in satisfactory manner until now, these problems relating to transporting a fluid in a microchannel, which is made difficult because of the reversibility of fluid mechanics at small scale, and also relating to providing valves capable of shutting off microchannels in leaktight manner.
Proposals have already been made to form microchannels in a flexible polymer, with pressure being applied thereon to close a channel by flattening it, thereby constituting a microvalve. It is also possible to form a peristaltic type pump by means of a series of three such valves which are actuated in a given order.
Other known solutions make use of an electric field for moving an ionized fluid (electro-osmosis) or charged particles (electrophoresis).
Another known solution consists in using electrical resistor elements to apply heat locally to an interface between two non-miscible fluids in order to cause one of the fluids to move by thermocapillary convection or the Marangoni effect.
Proposals have also been made to move materials and fluids by means of beads trapped in “multiple optical tweezers” generated by a narrowly focused light beams (work by K. Ladavac and D. Grier).
All of those solutions have drawbacks. Those that make use of the Marangoni effect have the advantage of creating an overall flow of fluid, but they are difficult to implement. Implementation makes use of electrical resistor elements placed on a microchannel fed with a first fluid in the vicinity of the outlet from another microchannel for bringing in a second fluid that is to form a bubble in the first fluid. The electrical resistor element(s) heat(s) one side of the interface between the two fluids to create a temperature gradient along the interface, thereby causing the first fluid to move towards lower temperatures, and thus inducing overall movement of the fluid in a determined direction (see document U.S. Pat. No. 6,533,951).
In that known technique, the heating resistor elements are integrated in the microfluidic circuit during manufacture, so that it is not possible to modify their locations and characteristics. Such integration also leads to an increase in the cost of the circuit. Furthermore, although it is easy to apply heat by powering the resistor elements, nothing is provided for cooling, and the pumping effect continues over a certain length of time after the power supply to the resistors has been stopped, until they return to ambient temperature.